Anti-reflective layer and method for manufacturing semiconductor device using the same

ABSTRACT

A method for manufacturing an anti-reflective layer comprises the steps of coating a polymer solution containing at least one compound selected from the group consisting of phenol-based resins, water-soluble resins and acryl resins as a main component, and then baking at a high temperature. The method is simplified and the layer&#39;s reflectance is greatly enhanced.

This is a division of application Ser. No. 08/136,833, filed Oct. 18,1993, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to an anti-reflective layer and method formanufacturing a semiconductor device using the same, and moreparticularly, to an anti-reflective layer formed by a using resistcomposition and a method for manufacturing a semiconductor device usingthe same.

It is well known that fine patterns of a semiconductor device are formedby using photolithography. A schematic method for manufacturing patternsusing the photolithography is as follows.

First, on a substrate desired to be patterned such as a semiconductorwafer, a dielectric layer or a conductive layer, a photoresist film madeof organic materials which has the characteristic of changing itssolubility to an alkaline solution before and after exposure toultraviolet (UV) light, X-ray radiation etc. is formed. The resist filmis selectively exposed by employing a mask pattern above the photoresistfilm, and then is developed to remove the portion having high solubility(in the case of a positive resist, removing the exposed portion) andleave the portion having low solubility to form resist patterns. Etchingthe substrate of the portion on which the resist has been removed toform patterns, and then removing the remaining resist, gives desiredpatterns for wiring, electrodes, etc.

Since fine patterns of high resolution can be obtained, the patterningmethod by the above-described photolithography is widely used. However,in order to form finer patterns, still further improvements in themanufacturing process are necessary.

The linewidth of the fine patterns formed after exposing and developingthe photoresist film is required to be the same with that of thephotomask at a particular reduction ratio. However, since many steps areneeded in photolithography, it is very difficult to keep the linewidthof the patterns consistent. The variation of the linewidth is mainly dueto a) the difference of exposing dosage owing to the difference of thethickness of resist, and b) light interference due to the diffusedreflection of the light over the topography (S. Wolf and R. N. Tauber,Silicon Processing for the VLSI Era, Vol.1, p439, 1986).

Recently, the miniaturization of systems utilizing complex integratedcircuitry has required chip-designed circuits of a far smaller size.Such a decrease in size, or an increase in capacity necessitates aminiaturization in the photolithography process, which could besatisfied with the use of more even topography and light of shorterwavelength.

However, the use of the higher frequency light as the exposure sourceresults in a new problem. For example, a KrF excimer laser and DUV (deepUV) light which are expected to be used for manufacturing 256M bit DRAM(dynamic random access memory) have a shorter wavelength than theg-line, i-line, etc. If such light is used as the light source, certaindefects, namely, those attributable to the reflections from a sub-layerhaving an uneven surface, become influential. That is, the CD differenceoccurs due to interference or a diffused reflection from the surfacehaving an uneven topography.

To solve the above-mentioned problems, the coating of an anti-reflectivelayer is considered inevitable.

An anti-reflective layer is disclosed in U.S. Pat. No. 4,910,122. Thelayer is employed under a photosensitive layer such as photoresist andserves to exclude the defects attributed to the reflected light. Thelayer contains light absorbing dye components and is formed as an evenand thin layer, so sharp photosensitive layer patterns can bemanufactured by employing such a layer since the layer may absorb thelight reflected from the substrate, as in a conventional method.

However, the conventional anti-reflective layer for DUV light hascomplicated components and limits in choosing materials. This raisesproduction cost and makes its application difficult.

As one example of the conventional anti-reflective coating composition,a six-component mixture composition of polygamic acid, curcumin, bixin,sudan orange G, cyclohexanone and N-methyl-2-pyrrolidone is disclosed inthe above-mentioned U.S. patent. This composition consists of fourcompounds of dye which absorb light of a specific wavelength and twosolvents to dissolve the four compounds. From the exemplifiedcomposition, it is known that the composition is quite complicated andits preparation is not an easy task. Moreover, since the compositionconsists of many components, the problem of intermixing with the resistcomposition coated on the surface of the anti-reflective layer occurs,resulting in an undesirable product.

SUMMARY OF THE INVENTION

One object of the present invention considering the above-mentioneddefects of the conventional anti-reflective coating composition, whileeliminating the complexity of the components constituting theconventional anti-reflective coating composition and enabling singlecomponent system, as well as reducing the production cost, is to providean anti-reflective coating composition containing novolak-based resin,water-soluble resin or polyvinylphenol-based resin which are known asraw materials of photoresists be fitting the g-line and/or i-line.

Another object of the present invention is to provide an anti-reflectivelayer using the coating composition of the present invention.

Further object of the present invention is to provide a method formanufacturing the anti-reflective layer of the present invention.

A still further object of the present invention is to provide a methodfor manufacturing a semiconductor device which is simple and gives goodproducts through employing the anti-reflective layer of the presentinvention.

To accomplish the object of the present invention there is provided inthe present invention an anti-reflective coating composition for asemiconductor device comprising polymer solution containing at least onecompound selected from the group consisting of phenol-based resins,water-soluble resins and acryl resins as a main component.

Another object of the present invention is accomplished by a method formanufacturing an anti-reflective layer comprising the steps of coating apolymer solution containing at least one compound selected from thegroup consisting of phenol-based resins, water-soluble resins and acrylresins as a main component and baking at a high temperature.

A further object of the present invention is accomplished by ananti-reflective layer manufactured by the above-mentioned method.

A still further object of the present invention is accomplished by amethod for manufacturing a semiconductor device comprising the steps offorming an anti-reflective layer through coating a polymer solutioncontaining at least one compound selected from the group consisting ofphenol-based resins, water-soluble resins and acryl resins as a maincomponent, and then baking at a high temperature, forming aphotosensitive layer on the surface of the anti-reflective layer andexposing and developing the photosensitive layer.

START

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects of the present invention will become more apparent bydescribing in detail a preferred embodiment thereof with reference tothe attached drawings in which:

FIG. 1 is a graph showing the reflectance of 248 nm light with respectto the baking temperature after coating an anti-reflective coatingcomposition during the manufacture of an anti-reflective layer accordingto the present invention.

FIG. 2 is a graph showing the relative intensity variation of FT-IR peakwith respect to the baking temperature during manufacture of ananti-reflective layer according to the present invention, in which "a"corresponds to about 1500 cm¹ peak, and "b" corresponds to about 1720cm¹.

FIGS. 3A and 3B are graphs showing the transmittances of anti-reflectivelayers with respect to the wavelengths of the UV light at various bakingtemperatures, in which (FIG. 3A) corresponds to the 150 nm thickanti-reflective layer made from a polymer composition composed ofnovolak-based resin+diazonaphtoquinone (DNQ)-based photoactive compound(PAC), and (FIG. 3B) corresponds to a 500 nm-thick anti-reflective layermade from novolak-based resin.

FIG. 4 is a graph showing the reflectance at 248 nm light, in which "a"corresponds to the case without employing an anti-reflective layer,while "b" corresponds to the case employing an anti-reflective layermade by the method of the present invention.

FIG. 5 is a graph showing the critical dimension (CD) variation of thepatterns formed by using 248 nm light, in which "a" corresponds to thecase without employing an anti-reflective layer, while "b" correspondsto the case employing an anti-reflective layer made by the method of thepresent invention.

FIG. 6 illustrates a process flow of manufacturing a semiconductordevice using the anti-reflective layer according to one embodiment ofthe present invention.

FIGS. 7A, 7B, 7C, 7D are SEM photographs showing the characteristics ofthe pattern at 300 nm steps manufactured by the conventional singleresist method, in which the linewidths of the patterns in A, B, C and Dare 0.30 μm, 0.32 μm, 0.34 μm, respectively, and 0.36 μm, and thethickness of the resists are all 0.5 μm.

FIGS. 8A and 8B are SEM photographs showing the characteristics of thepattern at 300 nm steps manufactured by employing an anti-reflectivelayer of the present invention, in which the thicknesses of the resistsin A and B are 0.5 μm and 0.8 μm, and the linewidths of the pattern areall 0.3 μm.

DETAILED DESCRIPTION OF THE INVENTION

An anti-reflective coating composition for a semiconductor device of thepresent invention comprises a polymer solution containing at least onecompound among phenol-based resins, water-soluble resins and acrylresins as a main component.

The preferred phenol-based resins include novolak-based resins,polyvinylphenol-based resins, a mixture thereof, or a copolymer-basedresin containing at least one compound thereof and the preferredwater-soluble resins include a polyvinylalcohol resin. The solvent forthe polymer solution may be any one that can dissolve the resincomponent, and at least one selected from the group consisting ofalcohols, aromatic hydrocarbons, ketones, esters and deionized watercould be desirably used.

For manufacturing an anti-reflective layer of the present invention, apolymer solution containing at least one compound selected from thegroup consisting of phenol-based resins, water-soluble resins and acrylresins as a main component is coated on a substrate and then the coatedpolymer solution is baked at a high temperature.

The high temperature baking is preferably carried out under an ambientor oxygen atmosphere at the temperature range of from 200° C. to 400° C.for 30 seconds to 5 minutes, and the preferred thickness of the coatedlayer after the high temperature baking is less than 1500 Å.

A soft baking process to remove the solvent may be carried out after thecoating process to form the anti-reflective layer but before the hightemperature baking, and is preferably carried out at 100° C. to 250° C.for 30 seconds to 5 minutes.

The thickness controlling process of the coating layer may be includedafter the soft baking and is preferably carried out by removing theupper portion of the coating layer before high temperature baking usingat least one solvent selected from the group consisting of alcohols,aromatic hydrocarbons, ketones, esters and deionized water.

The use of the polymer solution containing at least one of thephenol-based resins, water-soluble resins such as polyvinylalcohol, andacryl resins as a main component as in the present invention means thatthe conventional resist could be used. The present invention ischaracterized in that a baking process is employed to impart thelight-absorbing function to the resin. The high temperature bakinginduces thermal reaction of each resin, and through the thermalreaction, the molecular structure of the resin changes by oxidation andthen the resin can absorb the DUV light. Through the present invention,a thin film of the coated resin could be formed, and since the thicknessof the anti-reflective layer can be controlled, the efficiency of theanti-reflective layer can be optimized at steps especially anddifficulties occurring during an etching process can be minimized.

The particular basic steps of the method for manufacturing theanti-reflective layer according to the present invention is as follows.

First, a resin is coated on a substrate by a coating method such as aspin coating. Optionally, the resin may be first baked to remove thesolvent and remove the upper portion of the resin using a solvent suchas alcohols, aromatic hydrocarbons, ketones, esters, deionized water.The thickness of the resin can be controlled by controlling thetemperature during the first bake and solvent treating time, if needed.If a coating layer having a desirable thickness is obtained at the resincoating step, this process may not be needed. Next, high temperaturebaking is carried out so that the resin layer acquires light absorbingcharacteristics. Through this high temperature baking, the resin layeris endowed with anti-reflective characteristics.

The anti-reflective layer and effects obtained therefrom will bedescribed in detail referring to the attached drawings.

FIG. 1 represents the relation between baking temperature andreflectance of the resin. The anti-reflective layer was manufactured bythe same manner as described in Example 1. But that baking temperaturewas varied and then the reflectance at 248 nm was measured and plottedwith respect to the baking temperature.

From the figure, it can be known that the reflectance is maximum atabout 200° C. and gradually reduces as the baking temperature increases.At 300° C., it lowers to about 45% and the coating layer changes to a248 nm-light absorbing body. It is also known that as the bakingtemperature increases, a layer having a better anti-reflection effectcan be manufactured. According to the inventors' experiment, thepreferred baking temperature was found to range from 200° C. to 400° C.If the baking temperature is higher than 400° C., the resin is liable tochange to an undesirable constitution owing to phenomenon such as theburning of the resin, and if the baking temperature is lower than 200°C., the solvent in the coating layer is not completely removed andresults in an intermixing with the photoresist components coated on theanti-reflective layer afterward. Therefore, the above-mentionedtemperature range is preferred, with a more preferred temperature rangebeing from 260° C. to 320° C.

FIG. 2 is a graph showing the relative intensity variation of theFourier transform-infrared (FT-IR) peak with respect to the bakingtemperature during manufacture of the anti-reflective layer according toExample 1 (described later), in which "a" corresponds to about 1500 cm⁻¹peak, and "b" corresponds to about 1720 cm⁻¹.

From the plot "a" which represents the variation of 1500 cm⁻¹ peak withrespect to the baking temperature in this figure, it is confirmed thatthe peak gradually reduces as the temperature increases and abruptlyreduces above 260° C. Since the peak corresponds to the aromaticcarbon-carbon double bond, this means that the aromatic carbon-carbondouble bond decreases. Altogether, it is certain that the structure ofthe resin changes.

Meanwhile, from the plot "b" which represents the variation of 1720 cm⁻¹peak with respect to the baking temperature, it is known that the peakabruptly increases for temperatures above 260° C. and at temperaturesabove 300° C., the peak is the maximum on the contrary to the plot "a".Since the IR peak of the 1720 cm⁻¹ corresponds to the C═O bond, it isassumed that the C═O bond in the novolak resin structure increases. Thatis, the amount of oxygen in the resin increases through the baking andthis kind of change in molecular structure of the conventional novolakresin produces a transformed resin which has an enhanced characteristicof absorbing 248 nm light.

FIGS. 3A and 3B are graphs showing the transmittances at variouswavelengths of the anti-reflective layers in various bakingtemperatures, in which (FIG. 3A) corresponds to the 150 nm thickanti-reflective layer made from polymer composition composed ofnovolak-based resin+DNQ-based PAC, and (FIG. 3B) corresponds to the 500nm thick anti-reflective layer made from novolak-based resin.

From FIGS. 3A and 3B, it is found that the transmittance lowers (meaningthat resin absorbance increases) as the baking temperature increases.This effect comes from the resin baking. The anti-reflective layer ofthe present invention formed by baking at especially high temperaturehas the effect of absorbing at wide wavelength region.

The present inventors observed the transmittance changes for theanti-reflective layers formed from polymer consisting of novolakresin+DNQ-based PAC with a 150 nm thickness and from novolak resin with500 nm thickness. From the result, it can be found that the decrease ofthe transmittance was not due to the photosensitive material, DNQ butdue to the structure change of the novolak-based resin by thermalreaction.

Therefore, the photosensitive material, which is the major cost amongthe components of the conventional resist composition, need not beincluded in the anti-reflective coating composition of the presentinvention.

FIG. 4 is a graph showing the reflectance of the photoresist at 248 nmwavelength, in which "a" corresponds to the case without employing ananti-reflective layer, while "b" corresponds to the case employing ananti-reflective layer made by the method of the present invention.

The reflectance of the photoresist layer without employing baked resinas the anti-reflective layer is high, and the reflectance variation withrespect to the thickness also is large, with the maximum differencebeing 43%. However, the reflectance of the photoresist layer employingthe baked resin as the anti-reflective layer is low (less than 30%)throughout the whole thickness and the maximum variation is 10%.

FIG. 5 illustrates graphs showing the variation of CD (criticaldimension) of the pattern formed using 248 nm wavelength, in which "a"corresponds to the case without employing an anti-reflective layer,while "b" corresponds to the case employing an anti-reflective layermade by the method of the present invention.

From FIG. 5, it is confirmed that the CD variation for the patternsformed without employing the anti-reflective layer is large and themaximum is 0.16 μm, while the maximum CD variation for the patternsformed by employing the anti-reflective layer is 0.04 μm.

FIG. 6 illustrates a process flow of manufacturing a semiconductordevice using the anti-reflective layer according to one embodiment ofthe present invention. Referring to the FIG. 6, the preferred embodimentfor manufacturing a semiconductor device according to the presentinvention will be described with concrete numerical values.

First, an aluminum layer is formed on a substrate and then resin iscoated by a spin coating method on the aluminum layer. Then apply softbake at about 210° C. for about 50 seconds, and then at about 120° C.for about 50 seconds to remove solvents. Multi-step soft bake enhancesthe evenness of the layer.

Next, the upper portion of the resin layer is removed using a solventsuch as ethylcellosolve acetate by a puddling method and then theremaining layer is dried by spinning. This thickness controlling stepcould be omitted if not needed. Commonly, the thickness controlled layerthrough the surface removing has enhanced evenness. The thickness of thelayer can be easily controlled by regulating the baking temperatureaccording to the kind of solvent used.

After then, high temperature baking is carried out to give the resinanti-reflective function at 250° C. or more on a hot plate for 50seconds or more, for example, at 300° C. for about 90 seconds. Throughthis second baking, the resin is oxidized and becomes a light absorbingbody. As the temperature of this second baking increases, thereflectance reduces.

A resist pattern is formed on the thus-obtained anti-reflective layerthrough a conventional lithography process including resist coating,exposing, baking (post exposure bake or PEB), and developing. At thistime, the resist film and the anti-reflective layer could be patternedseparately by patterning the resist to form resist patterns and thenetching the anti-reflective layer using the resist pattern as a mask.Thereafter, the aluminum layer under the anti-reflective layer ispatterned by etching. The anti-reflective layer could be etched andpatterned during etching the aluminum layer.

The preferred embodiments of the present invention will be described indetail below.

EXAMPLE 1

On a silicon substrate, MC kasei BL-1, 2CP (trade name manufactured byMitsubishi kasei), a novolak-based resist, was spin coated at 5200 rpmfor 30 seconds give to a 1300 Å thickness. The coating layer was softbaked on a hot plate at 210° C. for 50 seconds, and then again for 50seconds at 100° C. to remove solvent. The thickness of the layer wasadjusted to 700 Å using ethylcellosolve acetate by a puddling method for60 seconds. A final baking step at 300° C. for 90 seconds gave ananti-reflective layer according to the present invention. Thereflectance to 248 nm light after baking was lowered to 45% of a baresilicon wafer.

Resist film was formed by a conventional method and resist patterns wereformed through exposing, developing, etc. Thereafter, an etching processwas carried out.

XP89131 (trade name manufactured by Shipley Co.) was used as aphotoresist and the thickness of the resist film was at least 0.8 μmsince its thickness will be decreased during etching. A Nikon EX1755stepper (trade name manufactured by Nikon Co., Ltd) using a KrF excimerlaser was used as the lightsource. An aqueous TMAH(tetrmethylammoniumhydroxide) solution was used as a developingsolution, and Cl₂ and O₂ were employed for etching the anti-reflectivelayer in a time etch manner.

Following the above conditions, L/S (line/space) dimension of 0.30 μmwas obtained, even for a 3000 Å step.

EXAMPLE 2

An anti-reflective layer of the present invention was manufactured bythe same manner as described in Example 1, except for usingpolyvinylphenol-based resist instead of novolak-based resist. Thereflectance was lowered to 45% under the same conditions.

EXAMPLE 3

An anti-reflective layer of the present invention was manufactured bythe same manner described in Example 1, except for using pure novolakresin instead of novolak-based resist. Here, the weight averagemolecular weight (Mw) was 6,000 and the Mw-to-Mn (weight averagemolecular weight to number average molecular weight) ratio was seven.The same effect as in Example 1 was obtained.

COMPARATIVE EXAMPLE

Resist patterns were formed by the same manner as described in Example 1except that the anti-reflective layer was not formed.

FIGS. 7A-7D are SEM photographs showing pattern characteristics for a300 nm step manufactured by the conventional single resist methodwithout employing an anti-reflective layer, in which the linewidths ofthe patterns are 0.30 μm, 0.32 μm, 0.34 μm and 0.36 μm, respectively,and the thicknesses of the resists are all 0.5 μm.

FIGS. 8A and 8B are SEM photographs showing pattern characteristics fora 300 nm step manufactured by employing an anti-reflective layer of thepresent invention, in which the thicknesses of the resists in FIG. 8Aand FIG. 8B are 0.5 μm and 0.8 μm, respectively, and the linewidths ofthe pattern are both 0.3 μm.

From FIGS. 7A-7D and 8A & 8B, it is confirmed that the resist patternsmanufactured by using the anti-reflective layer of the present inventionhas an even better profile.

As described above, the present invention relates to an anti-reflectivelayer employed to eliminate the defects caused by the reflection of theexposed light from the substrate. The problems of complex componentselection and high cost for the conventional anti-reflective layer aresettled, and since a single component can be employed, the solvent canbe selected easily. Also, a pattern having a good profile is obtained byusing the anti-reflective layer manufactured using the composition ofthe present invention, which ultimately makes it possible to producesemiconductor devices having good quality.

Moreover, since film thickness could be freely controlled during theforming of a coating layer, the effect of the anti-reflective layer canbe optimized especially at steps, and problems occurring during etchingafter photolithography process can be minimized.

While the present invention has been particularly shown and describedwith reference to particular embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe effected therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method for manufacturing an anti-reflective layer comprising the steps of:coating a polymer solution containing at least one compound selected from the group consisting of phenol-based resins, water-soluble resins other than aryl resins or phenol resins and acryl resins as a main component on a substrate; and baking the coated polymer solution at a high temperature under conditions to increase the amount of carbonyl groups present on said at least one compound.
 2. A method as claimed in claim 1, wherein said phenol-based resin is a novolak-based resin, a polyvinylphenol-based resin, a mixture thereof, or a copolymer-based resin containing at least one compound thereof.
 3. A method as claimed in claim 1, wherein said water-soluble resin is a polyvinylalcohol resin.
 4. A method as claimed in claim 1, wherein the solvent of said polymer solution is at least one selected from the group consisting of alcohols, aromatic hydrocarbons, ketones, esters and deionized water.
 5. A method as claimed in claim 1, wherein said baking is carried out under an ambient or oxygen atmosphere.
 6. A method as claimed in claim 1, wherein the thickness of said anti-reflective layer obtained after said baking is less than 1500 Å.
 7. A method as claimed in claim 1, said method further comprising the step of soft baking after said coating step to remove solvents.
 8. A method as claimed in claim 7, said method further comprising the step of the thickness controlling of the coating layer after soft baking.
 9. A method as claimed in claim 8, wherein said thickness controlling step is carried out by removing the upper portion of the coating layer using at least one solvent selected from the group consisting of alcohols, aromatic hydrocarbons, ketones, esters and deionized water.
 10. A method according to claim 1, wherein the baking temperature is low enough and duration of baking is short enough to avoid burning the polymer.
 11. A method according to claim 1, wherein said baking step is carried out under an atmosphere containing oxygen.
 12. A method according to claim 11, wherein said baking step is conducted such that a thermal oxidation reaction occurs in said at least one compound whereby a light-absorbing characteristic of said at least one compound is increased.
 13. A method for manufacturing an anti-reflective layer comprising the steps of:coating a polymer solution containing at least one compound selected from the group consisting of phenol-based resins, water-soluble resins other than aryl resins or phenol resins and acryl resins as a main component on a substrate; and baking said coating at a temperature range of from 200° C. to 400° C.
 14. A method as claimed in claim 13, wherein said baking is carried out under an ambient or oxygen atmosphere.
 15. A method according to claim 13, wherein said baking step is conducted for from 30 seconds to 5 minutes.
 16. A method for manufacturing an anti-reflective layer comprising the steps of:coating a polymer solution containing at least one compound selected from the group consisting of phenol-based resins, water-soluble resins other than acryl resins or phenol resins and acryl resins as a main component on a substrate soft baking said coating at a temperature range of 100° C. to 250° C. to remove solvents and baking the coated polymer solution at a high temperature under conditions to increase the amount of carbonyl groups present on said at least one compound.
 17. A method as claimed in claim 16, said method further comprising the step of the thickness controlling of the coating layer after soft baking.
 18. A method according to claim 16, wherein said soft baking step is conducted for 30 seconds to 5 minutes.
 19. A method for manufacturing an anti-reflective layer comprising the steps of:coating a polymer solution comprising a novolac resin as a main component on a substrate; and baking the coated polymer solution at a temperature high enough and under conditions to increase the amount of carbonyl groups in the novolac resin, and wherein the temperature is low enough and duration of baking is short enough to avoid burning of the novolac resin.
 20. A method for manufacturing an anti-reflective layer comprising the steps of:coating a polymer solution containing at least one compound selected from the group consisting of phenol-based resins, water-soluble resins other than acryl resins or phenol resins and acryl resins as a main component on a substrate; and baking said coating at a temperature from 260° C. to 320° C.
 21. A method according to claim 20, wherein said baking step is conducted for from 30 seconds to 5 minutes. 